The present invention relates to an automatic transmission comprising a transmission mechanism including plural planetary gear sets, and an adjusting method of a gap in an axial direction of the automatic transmission.
In general, an automatic transmission for an automotive vehicle is manufactured by assembling a transmission mechanism, such as planetary gear sets, clutches, and brakes, to a cylindrical transmission case. Plural parts of the transmission mechanism are assembled in an axial direction through an opening of the transmission case located on a side opposite to a torque converter in a specified order, and eventually an end cover is disposed so as to close the opening of the transmission case. In case there is a partition wall to divide the inside of the transmission case into two parts in the axial direction, such parts may be assembled toward the partition wall in the axial direction from both sides. Accordingly, the more the parts number is, the longer the manufacturing time becomes.
In order to reduce the manufacturing time, some parts may be assembled outside the transmission case as a subassembly, then the subassembly may be assembled into the transmission case. For example, Japanese Patent Laid-Open Publication No. 2007-078191 discloses an automatic transmission in which some parts including brakes, pistons and so on are assembled to the end cover to form such a subassembly.
Herein, many parts of the transmission mechanism of the automatic transmission are disposed side by side in the axial direction, so an entire axial length may tend to be too long or too short. In case the entire axial length is too long, a gap between the parts becomes so narrow that the lubricating oil may not be supplied into the gap sufficiently, resulting in an increase of friction generated between the parts. Meanwhile, in case the entire axial length is too short, the gap between the parts becomes so wide that there may occur improper shaking of the parts. Thus, the performance or durability of the automatic transmission would deteriorate in the above-described cases.
Herein, an adjustment of such gap in the axial direction may be conducted by using a washer which may be selected from plural washers which have different axial thicknesses from each other in order to cope with the above-described problems.
Specifically, at first, all parts of the transmission mechanism are assembled into the transmission case in such a manner that those are put aside toward one side in the axial direction to make the gap between parts minimum. Then, the axial location of one member of parts which is located on the other side is measured, and a proper washer having the appropriate axial thickness is selected based on the difference between the above-described measured axial location and an axial location of the member which is in a use state at the operation of the transmission case, that is, based on total gaps between the parts during the operation of the transmission case, thereby properly adjusting the gaps between the parts in the axial direction at the operation of the transmission case.
According to the automatic transmission of the above-described patent publication, however, the parts of the transmission mechanism are assembled separately to the transmission case and the end cover, so that all of the parts are not assembled into the transmission case until the end cover closes the opening of the transmission case. Accordingly, the measurement of the gap in the axial direction could not be conducted. Thus, the adjustment of the gap in the axial direction by using the washer could not be conducted easily.